Technology Development for Cryogenic Fluid Management, 18-9250

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Principal Investigators
Franklin T. Dodge
Steven T. Green
David B. Walter

Inclusive Dates: 04/01/01 - 09/30/02

Background - Reusable launch vehicles planned for the nation's future space program will be powered by cryogenic propellants, such as liquid oxygen and hydrogen because of their performance advantages. The advantages are offset, however, by the rudimentary state of the technologies needed to handle these fluids in a tank during low-gravity maneuvering. One critically needed technology is a method to ensure a flow of liquid, free of vapor, to the engine for re-starts when the liquid is floating in the tank away from the outlet. Screened channels (a flow channel that has one or more walls made of a fine mesh screen) are commonly used when the propellants are nonvolatile, such as kerosene. The screens allow liquid to enter the channel but block gas from entering. With a cryogenic propellant, however, a screened channel is susceptible to the generation of vapor within the channel by heat transfer, and when this generation occurs, further vapor can flow from the tank into the channel. This project developed an innovative tapered screened channel that automatically removes any vapor bubbles generated within the channel.

Approach - Laboratory experiments will be conducted on small tapered channels using a simulated cryogenic liquid. The channels will be horizontal and very shallow to eliminate buoyancy effects. The experiments will characterize the vapor-bubble-clearing action as a function of taper angle and fluid surface tension. Analytical models will be developed, based on first principles, to predict the channel fluid dynamics. The models will be validated by comparing their predictions to the experimental results.

Accomplishments - A large number of experiments were conducted with two small tapered channels having glass walls to allow visual observations. Gas bubbles were injected in the channels, and the motion of the bubbles were tracked as they moved under the influence of surface tension forces to the wider end of the channels. The top illustration shows such a bubble in one of the channel, in this case having a 5° taper. The second illustration shows typical measurements. The analytical model showed that the bubble velocity depended on the taper angle and the size of the bubble. The model not only predicted the trends of the data shown in the second illustration but it also agreed with the measurements quantitatively. With these test results and analytical models, tapered screened channels can be designed with confidence for reusable launch vehicles employing cryogenic propellants

Test of tapered channel showing bubble motion toward wide end.
 
Test results showing vapor bubble cleaning for two different bubbles sizes.

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